1. Field of the Invention
This invention pertains to laser resonator systems. Specifically, the present invention is for a method and means for correcting thermally induced stress birefringence in laser resonators.
2. Description of the Prior Art
Birefringence or double refraction is the splitting of a beam of light into two components which travel at different velocities. This phenomena is normally induced as a consequence of thermal stress in solid state laser devices, such as laser crystals. A laser rod, such as a yttrium aluminum garnet crystal doped with neodymium ions, known as a Nd:YAG, must dissipate significant amounts of heat. The cylindrical geometry of such rods leads to a radial temperature gradient with the highest temperature at the center of the rod and the coolest temperature on the surface of the rod where cooling occurs. This temperature gradient generates thermal stresses causing compression within the rod and tension at the surface. Different geometries of rods merely give rise to different shaped thermal gradients.
Numerous patents have been awarded for techniques to correct birefringence. Some of these techniques provide limited compensation of the birefringence by introducing equal and opposite thermal stresses into the rod itself. Others have had various types of components inserted into the resonating cavity to rotate the plane of polarization or to mechanically apply equal and opposite stresses. In general, these devices have only had limited success. The limited success is because there are numerous factors creating the birefringence, while each component disclosed previously has been designed to deal with a specific factor in causing the birefringence.